A particle size of sediment is a basic physical parameter which has an influence on entrapment, transportation and deposition by sediment transportation medium. Therefore, the particle size of the sediment is basic data which allows an analogy to the origin, transportation path and deposition condition of the sediment.
The particle size which is generally referred in a sedimentology is measured directly using a caliper in a case of gravel, through a dry and wet sieving in a case of sand, and using a difference in deposition speeds based on the Stoke's law in a case of fine sediment having a particle size of less than the size of silt (less than 63 μm).
Therefore, in actual samples, the particle size is mostly measured using at least two methods. Since the measuring method is varied as a particle class, the particle size actually represented by the method may include a maximum caliper diameter, a sieve diameter and a diameter of a quartz ball which is hydraulically equal.
That is to say, in a particle size analysis of geological sediment, the problem is a statistical processing of heterogeneous measured values as well as ambiguities and disagreements in the physical properties represented by the measured value which is a fundamental problem.
Therefore, a result of the particle size analysis which is expressed by percent by weight or percent by volume of particles in each class could be statistically processed and interpreted more coherently than the present if the measuring method is identical irrespective of the class.
Since most sediment is composed of sand and mud, if a satisfactory result is obtained by a method capable of measuring simultaneously the particle sizes of the sand and the mud, it would be possible not only to reduce the ambiguities in the particle size analysis for the sediment but also to reduce time and efforts taken into a particle size measuring process according to the deposition method.
In a case of sandy sediment, it is possible to separate particles having a diameter of more than 63 μm (4Φ) by the dry and wet sieving, but it is inefficient to separate particles having a diameter of less than 125 μm (3Φ) for a dry sample.
In a case of muddy sediment, in order to utilize a pipette method according to the Stoke's law, it is necessary to satisfy a rigid condition that the particles having a diameter of at least less than 50 μm (silt) should be dispersed to less than 1%.
Besides this principal restriction factor, there is a problem that much time and efforts are taken for a pre-process such as removal of organic substances and a post process such as drying and weighing of the sample in order to employ these methods.
Therefore, it has been a long desire of the researchers to develop a particle size analyzer which can eliminate an error according to an experimenter and easily complete a particle size analysis of the sample by measuring the particle size of the sandy and muddy sediments at a time through a minimum preprocess.
In a measurement of a particle size of the sediment including from fine particles of several μm to coarse particles of thousands μm, the most important challenge for obtaining a reliable result in the particle size analysis is to prevent the coarse particles from being sunken by the gravity and to obtain uniform mixing of the particles.
General wet-type particle size analyzer is mostly for particle size analysis of fine particles, and thus the mixing of the sample is conventionally carried out by microwave vibration of a mixing reservoir within the particle size analyzer and recirculation which is limited to an inside of the particle size analyzer. This mixing method is efficient for the particles having a fine size (several μm), but it is impossible to obtain the uniform mixing in the case of coarse particles.
When the sample mixing part is separated from the wet-type particle size analyzer and a mixture liquid is supplied to the particle size analyzer by a recirculation system, it is possible to measure more coarse particles. However, such analyzer also has a limitation that a uniform mixture liquid cannot supplied to the particle size analyzer in the case that a large amount of the coarse particles is included since there has been almost no study for an analyzer which measures all ranges of particle size.